The present invention relates generally to water-soluble, chiral interpolymer complexes containing a conducting polymer and, more particularly, to a chemical method for synthesizing such chiral interpolymer complexes.
Polyaniline has received increased interest for industrial applications (See, e.g., xe2x80x9cPlastics that Conduct Electricityxe2x80x9d by R. B. Kaner and A. G. MacDiaramid, Scientific American 258, 106 (1988)). Chiral conducting polymers are particularly interesting for industrial applications including surface-modified electrodes, chemical separation materials, self assembled monolayers, light emitting devices, light filters (Bragg filters), and liquid crystalline devices, to name a few examples. Chiral polyaniline has been generated. In xe2x80x9cChemical Generation Of Optically Active Polyaniline Via The Doping Of Emeraldine Base With Camphorsulfonic Acidxe2x80x9d by M. R. Majidi, et. al., Polymer 36, 3597 (1995), it was disclosed that optically inactive polyaniline could be converted to optically active polyaniline by dissolving the emeraldine base form of polyaniline (EB) in n-methyl-2-pyrrolidinone and adding either (+)- or (xe2x88x92)-CSA. More recently, chiral polyaniline was electrochemically synthesized by polymerizing an aqueous solution of aniline in the presence of either (+)- or (xe2x88x92)-CSA (See e.g., xe2x80x9cFacile Preparation Of Optically Active Polyanilines Via The In Situ Chemical Oxidative Polymerization Of Anilinexe2x80x9d by I. D. Norris et. al., Synthetic Metals 106, 171 (1999)). The optically active polyanilines were found to be insoluble in common solvents and, consequently, difficult to process and difficult to purify.
U.S. Pat. No. 6,090,985 for xe2x80x9cChiral Polyanilines And The Synthesis Thereofxe2x80x9d which issued to Alan G. MacDiarmid, et al. on Jul. 18, 2000 describes the chemical synthesis of chiral polyanilines which includes polymerizing an aniline monomer in the presence of a chiral dopant acid, an oxidizing agent and, optionally, a substrate. The products of this synthesis are not water-soluble. Furthermore, existing chiral materials are susceptible to loss of their optical activity. One might expect that if the chiral dopant is removed (by solution phase dedoping) the organized chiral conformation PAN will be susceptible to thermal randomization. Indeed, when a solid film of chiral emeraldine base is dissolved in organic solvents, the optical activity is lost (See, G. G. Wallace et al., Macromolecules, 33, 3237-3243 (2000)). Wallace et al. synthesized chiral polyaniline by dissolving both polyaniline emeraldine base and optically active camphorsulfonic acid in a common organic solvent, n-methyl-2-pyrrolidinone. The optical activity is also lost when a chiral PAN.CSA is heated to eliminate CSA (See, I. D. Norris et al., Macromolecules 31, 6529-6533 (1998)).
Water-soluble, chiral polyaniline nanocomposites have been synthesized by electrochemically polymerizing aniline in the presence of optically pure CSA and a dispersant, either polystyrene sulfonate or colloidal silica (See, e.g., xe2x80x9cElectrochemical Formation Of Chiral Polyaniline Colloids Codoped With (+)- Or (xe2x88x92)-10-Camphorsulfonic Acid And Polystyrene Sulfonatexe2x80x9d by J. N. Barisci et al., Macromolecules, 31, 6521 (1998); xe2x80x9cPreparation of Chiral Conducting Polymer Colloidsxe2x80x9d by J. N. Barisci et al., Synthetic Metals, 84, 181 (1997); and xe2x80x9cElectrochemical Preparation Of Chiral Polyaniline Nanocompositesxe2x80x9d by V. Aboutanos et al., Synthetic Metals, 106, 89 (1999).). Also, a self-doped, water-soluble, chiral polyaniline has been synthesized by electrochemically polymerizing a 2-methoxyaniline-5-sulfonic acid monomer in the presence of (+) or (xe2x88x92) CSA (See xe2x80x9cOptically Active Sulphonated Polyanilinesxe2x80x9d by E. V. Strounina et al., Synthetic Metals, 106, 129, (1999)). These water-soluble complexes were all synthesized electrochemically. Electrochemical synthesis (See, e.g., Wallace et al., supra) is considered by industrial standards to be small-scale syntheses and is not as promising as chemical synthesis for large-scale production.
Sun et al. and Liu et al. achieved the template-guided synthesis of water-soluble non-chiral polyaniline complexes by polymerizing an aniline monomer in the presence of a polyelectrolyte (See, e.g., L. Sun et. al., American Chemical Society Polymer Preprints, 33, 379 (1992), L. Sun et. al., Materials Research Society, Society, Symposium Proceedings, 328, 209 (1994); L. Sun et al., Materials Research Society, Symposium Proceedings, 328, 167 (1994); and R. J. Cushman et al., Journal of Electroanalytical Chemistry, 291, 335 (1986)). The final product is a double-stranded polymer complex in which the polyaniline and the template (polyelectrolyte) are bound by electrostatic interaction (See, e.g., L. Sun et al., Synth. Metals 84, 67 (1997) and U.S. Pat. No. 5,489,400 for xe2x80x9cMolecular Complex Of Conductive Polymer And Polyelectrolyte; And A Process For Producing Samexe2x80x9d which issued to J. M. Liu et al. on Feb. 06, 1996). Such polyaniline complexes are water soluble because of the hydrophilic nature of the polyelectrolyte. The above references teach that template-guided syntheses are carried out stepwise. First, the template (a pre-formed polymer) and the monomer of the conducting polymer to be prepared are assembled into an adduct, the acidity of the adduct solution is then adjusted, and the polymerization is initiated.
Interpolymer complex syntheses have advantages over existing water-soluble polyaniline syntheses. In U.S. Pat. No. 6,018,018 for xe2x80x9cEnzymatic Template Polymerizationxe2x80x9d which issued to Lynne A. Samuelson et al. on Jan. 25, 2000, the enzymatic formation of polymers in the presence of a template is described wherein at least one physical property of the resulting polymer is affected. The method includes combining at least one redox monomer or, in some cases, a redox oligomer, with a template and an enzyme, such as horseradish peroxidase, to form a reaction mixture. The redox monomer or oligomer aligns along the template before or during the polymerization. The complex formed thereby can be electrically or optically active. Since enzymes are required, such syntheses are expensive and products therefrom are difficult to purify.
Accordingly, it is an object of the present invention to provide a method for chemically synthesizing water-soluble, chiral polyanilines without using electrochemistry, enzymes or chiral polymers.
Another object of the invention is to provide a method for chemically synthesizing water-soluble, chiral polyanilines that can be carried out on a large scale and the resulting product easily purified.
Additional objects, advantages and novel features of the invention will be set forth, in part, in the description that follows, and, in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects of the present invention and in accordance with its purposes, as embodied and broadly described herein, the template-guided method for chemical synthesis of water-soluble, chiral conducting-polymer complexes hereof includes contacting a conducting polymer monomer with a chosen water-soluble polymer, thereby forming an adduct; contacting the adduct with a chiral acid, polymerizing the monomer, whereby a water-soluble, interpolymer complex containing a chiral conducting polymer bound to the water-soluble polymer is formed.
It is preferred that the monomer is aniline.
Preferably, the chiral acid is camphorsulfonic acid.
Preferably also, the water-soluble polymer is poly(acrylic acid).
It is also preferred that the ratio of added monomer to the template polymer repeating unit is between 0.001 to 10.
Benefits and advantages of the present invention include the inexpensive, straightforward preparation of stable, water-soluble, chiral, conducting-polymer complexes which can be scaled to industrial quantities. Increased conformational stability will be advantageous for industrial applications including; surface coating or membrane for separation of optical isomers. The interpolymer complex of this invention also remains optically active after repeated doping and de-doping cycles.